Don't consider threads for breaking continuation until actually created

src/components/structures/MessagePanel.tsx

@@ -66,6 +66,10 @@ const groupedEvents = [
     EventType.RoomPinnedEvents,
 ];
 
+function hasThreadSummary(event: MatrixEvent): boolean {
+    return event.isThreadRoot && event?.getThread().length && !!event.getThread().replyToEvent;
+}
+
 // check if there is a previous event and it has the same sender as this event
 // and the types are the same/is in continuedTypes and the time between them is <= CONTINUATION_MAX_INTERVAL
 export function shouldFormContinuation(
@@ -96,7 +100,7 @@ export function shouldFormContinuation(
 
     // Thread summaries in the main timeline should break up a continuation on both sides
     if (threadsEnabled &&
-        (mxEvent.isThreadRoot || prevEvent.isThreadRoot) &&
+        (hasThreadSummary(mxEvent) || hasThreadSummary(prevEvent)) &&
         timelineRenderingType !== TimelineRenderingType.Thread
     ) {
         return false;

test/components/structures/MessagePanel-test.js

@@ -699,7 +699,7 @@ describe('MessagePanel', function() {
 });
 
 describe("shouldFormContinuation", () => {
-    it("does not form continuations from thread roots", () => {
+    it("does not form continuations from thread roots which have summaries", () => {
         const message1 = TestUtilsMatrix.mkMessage({
             event: true,
             room: "!room:id",
@@ -730,6 +730,13 @@ describe("shouldFormContinuation", () => {
         });
 
         expect(shouldFormContinuation(message1, message2, false, true)).toEqual(true);
+        expect(shouldFormContinuation(message2, threadRoot, false, true)).toEqual(true);
+        expect(shouldFormContinuation(threadRoot, message3, false, true)).toEqual(true);
+
+        const thread = {};
+        thread.length = 1;
+        thread.replyToEvent = {};
+        jest.spyOn(threadRoot, "getThread").mockReturnValue(thread);
         expect(shouldFormContinuation(message2, threadRoot, false, true)).toEqual(false);
         expect(shouldFormContinuation(threadRoot, message3, false, true)).toEqual(false);
     });